PbO2形稳阳极的制备及其电催化氧化降解有机污染物的作用机制

发布时间：2017-12-26 18:18

  本文关键词：PbO2形稳阳极的制备及其电催化氧化降解有机污染物的作用机制　出处：《西安建筑科技大学》2017年博士论文　论文类型：学位论文

  更多相关文章： PbO2阳极材料 电催化氧化 难降解有机废水 离子液体 羟基自由基

【摘要】：电化学氧化技术被证实是去除废水中难降解有机污染物的有效方法,显示出良好的应用前景和发展潜力,成为当前工业废水处理领域的研究热点。发展电氧化技术的首要关键是高性能、低成本电极材料的开发。钛基PbO_2形稳阳极由于具有良好的导电和耐蚀性、较高的析氧过电位、较低的成本以及强氧化能力,成为被广泛研究和应用的阳极材料对象。为进一步改善PbO_2电极的电催化活性与稳定性,本论文提出将微量咪唑基离子液体(ILs)添加至电沉积溶液中,利用ILs特有的电化学性质与吸附性,对钛基PbO_2电极进行修饰改性制备,系统考察了ILs分子结构、添加浓度、沉积温度、电流密度等工艺条件对PbO_2电极涂层晶体结构、形貌及性能的影响特性;通过对PbO_2电沉积过程的原位电化学分析,以及ILs改性前后PbO_2涂层的微观晶体和电子结构的表征,分别从电极材料的制备及结构角度阐释ILs对PbO_2电极的改性机理,从而为应用于难降解有机废水处理领域的高性能阳极材料的制备提供借鉴。同时,对PbO_2电极氧化降解有机物过程中的羟基自由基(·OH)检测方法、产生规律及影响因素进行了系统研究,确立了降解过程中·OH生成量与有机物降解效率、历程的内在联系,为电氧化生物难降解有机污染物作用机制的阐释提供了事实依据。论文研究丰富了环境电化学的内容,为电化学法处理有机污染物提供了理论基础和技术支持,主要研究工作和结论如下:(1)将1-乙基-3-甲基-咪唑四氟硼酸盐([Emim]BF4)添加到Pb(NO3)2混合电积溶液中,通过阳极氧化电沉积法可以制备得到结晶良好、晶粒大小均匀、表面致密平整的钛基β-PbO_2形稳阳极材料。考察获得主要制备工艺的优化条件为:[Emim]BF4添加浓度为50 mg/L、温度50℃、电流密度10 mA/cm2。PbO_2电极的电催化活性与其晶体结构密切相关,β-PbO_2比α-PbO_2具有更高的有机物降解活性;β-PbO_2的结晶度越高,活性越好;沿(110)晶面择优取向的β-PbO_2相比无择优取向或其他晶面择优取向的β-PbO_2显示出更高的电催化活性。(2)相比采用Fˉ和十二烷基磺酸钠(SDS)对PbO_2电极进行修饰改性的一般制备方法,由ILs辅助制备的PbO_2电极涂层结晶度更高、结晶取向亦发生明显改变,在10 mA/cm2下恒流电解180 min时,苯酚模拟废水的COD去除率相比一般方法制备的PbO_2电极提高了近20%。电极的电流效率在电解初期为38%,比后者高出15%左右。ILs辅助制备得到的PbO_2电极稳定性与一般方法制备的电极相比亦明显提高,加速寿命增加了近2倍。这些试验结果说明,利用ILs可以影响PbO_2电沉积过程,获得性能显著改善的钛基PbO_2涂层电极。(3)PbO_2电结晶按照三维生长和连续成核方式进行,ILs的加入没有改变其电结晶方式,但增加了阳极极化,对PbO_2形核和核生长均产生抑制作用,且以抑制核生长为主,最终导致晶核密度增加,得到致密的PbO_2涂层。此外,ILs辅助电沉积制备得到的钛基PbO_2涂层相比未改性电极表面致密规整、结晶度和晶格氧含量更高、表面氧空位含量明显降低。由此提出ILs对PbO_2电极修饰改性的机理在于使其晶体中氧空位含量明显减少,从而降低了氧化物电极表面高活性·OH向活性较差的晶格氧(Olat)衍变的发生几率。(4)研究对比了水杨酸(SA)和4-羟基苯甲酸(4-HBA)这两种不同·OH捕获剂的捕获效率差异,结果表明,电化学体系中SA的主要羟基化产物为2,5-DHBA,而产物2,3-DHBA和儿茶酚的含量非常小,可忽略不计。SA和4-HBA两种·OH捕获剂都具备羟基化产物单一、稳定的特点。SA和4-HBA与·OH的电化学氧化反应均符合一级反应动力学,反应速率常数k分别为2.1833×10-4 s-1和1.3500×10-4 s-1。要达到相同的·OH捕获量,4-HBA需3倍于SA的初始用量、约2.3倍于SA的捕捉时间。因此,SA比4-HBA具有更高的灵敏度和更强的?OH捕捉能力,进而建立了以SA为·OH捕捉剂,以高效液相色谱为检测手段的稳定可靠的·OH检测方法。(5)电极材料的电催化活性主要由其产生·OH的能力所决定。电解液中支持电解质对体系中·OH生成量的影响不明显,主要通过其在阳极氧化生成的氧化剂参与有机物的降解,以NaCl为支持电解质时降解效率最高,其次是Na_2SO_4,最后为NaNO3;随电解液pH值的增加,苯酚废水的COD去除速率不断提高,且·OH的生成量在碱性条件下亦显著增加;升高电解温度时,苯酚废水的COD去除率反而下降;增大电流密度会相应明显提高COD去除率;随着脉冲频率与占空比的增加,苯酚废水COD去除率均呈现先升高后下降的规律,在脉冲频率为500Hz、占空比为50%时达到最高。比较发现,采用脉冲电源时单位COD处理能耗相比直流电源可降低44%,具有明显节能效果。电解液性质和操作条件对·OH生成量的影响与其对苯酚废水COD去除率的影响规律基本一致,表明电氧化体系参数通过影响产生及进入到电解体系中的·OH量而影响电氧化效率,·OH的生成量与PbO_2电极对苯酚的电化学氧化降解效率密切相关。(6)PbO_2电极上苯酚模拟有机废水的COD去除符合一级反应动力学规律,加入·OH淬灭剂叔丁醇后COD去除率急剧下降,氧化反应速率常数降低了45%,充分证明了苯酚的电化学氧化降解遵循·OH反应机理。根据苯酚电氧化过程中间产物分布情况,推测苯酚在·OH的进攻下生成对苯醌、间(邻)苯二酚及马来酸等中间产物,随着电氧化反应的进行,中间产物亦被氧化去除而逐渐减少,最终实现有机物的完全降解。在含苯酚水溶液的循环伏安曲线中出现苯酚的氧化峰,说明苯酚的降解过程中存在直接电氧化作用。由此推断,PbO_2电极对苯酚有机污染物的电化学氧化降解作用机制是直接氧化(电子转移)与间接氧化(·OH氧化)共同作用的结果,其中·OH的间接氧化作用起绝对主导作用。(7)应用电催化氧化技术处理初始COD值为1009 mg/L的实际焦化废水时,升高温度、增大电流密度、增加支持电解质Na_2SO_4添加浓度等均有利于COD的去除。综合考虑处理效果和成本,较适宜的电流密度范围是20~30 mA/cm2;较适宜的Na_2SO_4用量是0.25 mol/L。脉冲电解相比直流电解能够降低能耗约35%。在40 mA/cm2,30℃、0.25 mol/LNa_2SO_4的操作条件下降解3 h时后,焦化废水的COD去除率达到90%以上,出水COD值可以达到国家一级排放标准值,此时单位COD处理能耗为178 kWh/kg。
[Abstract]:Electrochemical oxidation technology has been proved to be an effective way to remove refractory organic pollutants in wastewater. It shows good application prospects and development potential and has become a research hotspot in the field of industrial wastewater treatment. The key to the development of Electrooxidation is the development of high performance and low cost electrode materials. Titanium based PbO_2 stabilized anode has been widely studied and applied as anode material because of its good conductivity and corrosion resistance, high oxygen evolution overpotential, low cost and strong oxidation capacity. To further improve the electrocatalytic activity and stability of PbO_2 electrode, this paper will trace imidazolium ionic liquids (ILs) added to the electrodeposition solution, the electrochemical properties and adsorption of ILs specific and modified preparation of titanium based PbO_2 electrode, the effect of characteristics of ILs molecular structure, concentration the temperature, current density, deposition conditions of PbO_2 electrode coating crystal structure, morphology and properties of PbO_2; by in situ electrochemical deposition analysis, and ILs characterization of PbO_2 coating micro crystal and electronic structure of ILs before and after modification mechanism explanation respectively from the preparation of the electrode material and structure angle on the PbO_2 electrode, thus high performance anode material is used in treatment of refractory organic wastewater in the field of preparation of reference. At the same time, the hydroxyl radical PbO_2 electrode oxidation degradation of organic compounds in the process (OH) production rules and influence factors of detection method and system research, established the relationships in the degradation process of OH generation and degradation efficiency, process of organic matter, provide the basis for the electro oxidation of bio refractory organic pollutants the mechanism of interpretation. This study enriches the content of environmental electrochemistry, provides a theoretical basis and technical support for the electrochemical treatment of organic pollutants, the main research work and conclusions are as follows: (1) 1- ethyl -3- methyl imidazole tetrafluoroborate ([Emim]BF4) added to Pb (NO3) 2 mixed electrolyte, by anodic oxidation and electro deposition can be prepared with good crystallinity and uniform grain size, surface smooth titanium based anode material -PbO_2 beta shape stability. The optimization conditions of the main preparation process are as follows: the concentration of [Emim]BF4 is 50 mg/L, the temperature is 50, and the current density is 10 mA/cm2. PbO_2 is closely related to the electrocatalytic activity of the electrode and its crystal structure, beta -PbO_2 has organic matter degradation activity higher than alpha beta -PbO_2 -PbO_2; the crystallization degree is higher, the better the activity; (110) the preferential orientation of the beta -PbO_2 compared with no preferred orientation or other preferential orientation of the beta -PbO_2 show power higher catalytic activity. (2) compared with F - and twelve sodium dodecyl sulfate (SDS) on PbO_2 electrode preparation method modified by ILs, assisted preparation of PbO_2 electrode coating crystallinity and higher crystallinity also changed, electrolytic 180 min under 10 mA/cm2 constant current, the phenol wastewater the removal rate of COD compared with PbO_2 electrode preparation method generally has increased by nearly 20%. The current efficiency of the electrode is 38% at the initial stage of electrolysis, which is about 15% higher than that of the latter. The stability of the PbO_2 electrode prepared by ILs is also significantly higher than that of the electrode prepared by the general method, and the accelerated life of the electrode has increased by nearly 2 times. These results show that ILs can affect the PbO_2 electrodeposition process and obtain a titanium based PbO_2 coating electrode with remarkable improvement in performance. (3) PbO_2 crystal according to three-dimensional growth and continuous nucleation, the addition of ILs did not change the electric crystal, but increased the anodic polarization of PbO_2 nucleation and nucleus growth inhibition were produced, and the inhibition of nuclear growth, resulting in increase of nucleus density, obtain dense PbO_2 coating. In addition, the PbO_2 coating prepared by ILs assisted electrodeposition process is more regular than that of the modified electrode, and the crystalline and lattice oxygen content is higher, and the surface oxygen vacancy content is significantly reduced. It is suggested that the mechanism of modification of PbO_2 electrode by ILs is to decrease the content of oxygen vacancies in the crystals, thereby reducing the probability of evolution of lattice oxygen (Olat) on the surface of oxide electrodes with high activity and OH. (4) the difference of capture efficiency between two different OH capture agents of salicylic acid (SA) and 4- hydroxybenzoic acid (4-HBA) was studied and compared. The results showed that the main hydroxylated product of SA was 2,5-DHBA, while the content of 2,3-DHBA and catechol was negligible. Both SA and 4-HBA two OH capture agents have the characteristics of single and stable hydroxylation products. The electrochemical oxidation of SA and 4-HBA and. OH conforms to the first order reaction kinetics. The reaction rate constant k is 2.1833 x 10-4 S-1 and 1.3500 x 10-4 s-1, respectively. To achieve the same amount of OH capture, 4-HBA needs to be 3 times the initial amount of SA and about 2.3 times the capture time of SA. Therefore, SA has higher sensitivity and stronger OH capture ability than 4-HBA. Therefore, a stable and reliable OH detection method based on SA OH capture agent and high performance liquid chromatography is established. (5) the electrocatalytic activity of the electrode material is mainly determined by its ability to produce OH. The electrolyte support effect of electrolyte on the system content of OH is not obvious, mainly through its oxidative degradation agent by anodic oxidation in organic matter, with NaCl as the supporting electrolyte degradation efficiency is the highest, followed by Na_2SO_4, the last is NaNO3; with the increase of the pH value of the electrolyte, phenol removal rate constant COD to improve the production of OH, and also increased significantly under alkaline conditions; higher electrolysis temperature, phenol removal rate of COD decreased; the increase of current density will significantly improve the removal rate of COD; with the pulse frequency and duty ratio increases, the removal rate of COD phenol wastewater were increased and then decreased. In, 500Hz pulse frequency and duty ratio of 50% reached the highest. It is found that pulse electricity is used in comparison
【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X703
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